Accessibility considers whether or not—and to what extent—a product or service can be used by everybody. Designing for accessibility means factoring in the needs of people with disabilities, as well as the various ways in which a person might interact with your product (for example, using assistive technology).
Accessibility refers to the ability for any person, in any circumstance, using any device to access content on the web, including people with disabilities and is of increasing concern to organizations for financial, moral and legal reasons.